(1) Field of the Invention
The present invention relates to a gyrotron device for generating microwaves and, more particularly, to a gyrotron device which comprises a coaxial resonator for converting energy of an electron beam into energy of an electromagnetic wave.
(2) Description of the Related Art
FIG. 1 shows a basic arrangement of a conventional gyrotron device for generating microwaves.
The gyrotron device comprises electron gun cathode 1 for emitting an electron beam, anode electrode 2 for controlling the electron beam emitted from cathode 1, magnet coils 3, 4 for applying a magnetic field to cause electrons of the electron beam to produce cyclotron motions, cavity resonator 5 for receiving the electrons of the electron beam and resonating them with microwaves so as to generate microwaves, collector 6 for collecting the electrons, dielectric output window 7 and output waveguide tube 8 for cooperatively outputting the generated microwaves.
In the above-described gyrotron device, electrons emitted from electron gun cathode 1 are controlled by anode electrode 2, and the cyclotron motions of the electrons are produced in the magnetic field of the magnet coils 3, 4. When the electrons pass through cavity resonator 5, their energy is converted into microwave energy by being resonated with the microwaves. The electrons which pass through cavity resonator 5 are collected by collector 6. The generated microwaves are passed through dielectric output window 7 and are output along output waveguide tube 8.
The gyrotron device, in general, generates microwaves by cyclotron resonance coupling between the electrons of which are displaying the cyclotron motions and the microwaves which are generated by cavity resonator 5. In the gyrotron device comprising cavity resonator 5, if a frequency of the microwaves is set high, a resonance frequency between the microwaves and the electrons in cavity resonator 5 is also high. When the resonance frequency is high, the inner diameter of cavity resonator 5 is limited so as to be small. For this reason, an inner wall area of cavity resonator 5 is minimized, so that the inner wall surface of cavity resonator 5 is heated to a high temperature by joule heat. Therefore, if high-output microwaves of a higher frequency are generated, the inner wall surface of cavity resonator 5 is heated to an extremely high temperature, which causes thermal deformation and destruction of the cavity resonator 5 which cannot withstand the heating. Therefore, it is difficult to realize the gyrotron device for oscillating the high-output microwaves of a high frequency.